Jaime H Hoyos B - Academia.edu (original) (raw)
Papers by Jaime H Hoyos B
We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic... more We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term behavior of a non-uniform magnetic field in a one-dimensional geometry. Our main focus is the dissipation of magnetic energy inside neutron stars (particularly magnetars), but our results have a wider application, particularly to the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays (or ionization-recombination processes). In the "weak-coupling" limit of infrequent inter-particle interactions, the evolution of the magnetic field is controlled by the beta decay rate and can be described by a nonlinear partial integro-differential equation. In the opposite, "strong-coupling" regime, the evolution is controlled by the inter-particle collisions and can be modelled through a non-linear diffusion equation. We show numerically that, in both regimes, ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic field gradients with associated current sheets around those regions where the magnetic field is weak.
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying... more In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are “Hall equilibria”, i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an attractor ...
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying... more In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are "Hall equilibria", i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an ...
Neutron stars are compact objects remaining of supernova explosions. Astronomical observations su... more Neutron stars are compact objects remaining of supernova explosions. Astronomical observations suggest that surface star magnetic fields decay over long dissipative time scales. Although it is well known that the diffusive time scales are much longer than the age of the universe, non linear processes such as ambipolar diffusion or Hall effect can generate small-scale structures that shorten the time scales [1]. In this paper we calculate the magnetic diffusion modes confined in spherical neutron star crusts with axial symmetry (2D). The solution of the partial differential equations is based on a spectral method that expands the angular functions in Legendre polynomials while the radial and temporal part are solved by separation of variables.
American Journal of Physics, 2020
We provide a guide to implementing the particle-in-cell algorithm, which is useful for simulating... more We provide a guide to implementing the particle-in-cell algorithm, which is useful for simulating diverse phenomena in plasmas. We focus on two-dimensional systems which have vector fields with three Cartesian components but depend only on two spatial coordinates. We describe the algorithm in detail, including particle-to-grid interpolation, the fast Fourier transform, the Boris algorithm, and the use of dimensionless units. As an example, we discuss a simulation of the two-stream instability, which occurs in a plasma system composed of two counter-streaming electrons and an ion background at rest.We provide a guide to implementing the particle-in-cell algorithm, which is useful for simulating diverse phenomena in plasmas. We focus on two-dimensional systems which have vector fields with three Cartesian components but depend only on two spatial coordinates. We describe the algorithm in detail, including particle-to-grid interpolation, the fast Fourier transform, the Boris algorithm, and the use of dimensionless units. As an example, we discuss a simulation of the two-stream instability, which occurs in a plasma system composed of two counter-streaming electrons and an ion background at rest.
We present here a comprehensive model for the evolution of the magnetic properties of habitable t... more We present here a comprehensive model for the evolution of the magnetic properties of habitable terrestrial planets (Earth-like planets, M ∼ 1 M ⊕ and super-Earths M ∼ 1 − 10 M ⊕) and their effects on the long-term protection against the atmospheric erosive action of stellar wind. Using up-to-date thermal evolution models and dynamo scaling laws we predict the evolution of the planetary dipole moment as a function of planetary mass and rotation rate. Combining these results with models for the evolution of the stellar wind, stellar XUV fluxes and exosphere properties of highly irradiated planets, we determine the properties of the planetary magnetosphere and the expected scale height of the atmosphere that together determine the level of thermal and non-thermal atmospheric mass losses. We have used this model to evaluate the early magnetic protection of the Earth and the already discovered potentially habitable super-Earths GJ 667Cc, Gl 581d and HD 85512b. We confirm that Earth-like planets, even under the highest attainable dynamo-generated magnetic field strengths, will lose a significant fraction of their atmospheres or their content of critical volatiles (e.g. H 2 O) if they are tidally locked in the HZ of dM stars. Planets in this mass-range with N/O-rich atmospheres, even under the best conditions of magnetic protection, will probably lose their atmospheres or their water content if they are in habitable zones closer than ∼ 0.8 AU (M ⋆ 0.7 − 0.9M ⊙). Super-Earths M p 3M ⊕ seem to have better chances of preserving their atmospheres even if they are tidally locked around dM stars. Under similar conditions of thermal and magnetic field evolution there seems to exist a planetary mass-dependent inner limit inside the HZ itself, below which large atmospheric mass-losses in super-Earths are expected. With the nominal value of the physical parameters in our conservative model this limit is, for example, ∼0.1 AU for 4M ⊕ and ∼0.04 AU for 8M ⊕. Under these conditions we predict that the atmosphere of GJ 667Cc has probably already been obliterated and it is presently uninhabitable. On the other hand, our model predicts that the atmospheres of Gl 581d and HD 85512b would be well protected by dynamo-generated magnetic fields even under the worst expected conditions of stellar aggression.
Journal of Geophysical Research, 2003
In a previous paper, sufficiently large-amplitude and left-handed ''pump waves'' propagating para... more In a previous paper, sufficiently large-amplitude and left-handed ''pump waves'' propagating parallel to the background magnetic field were shown to stabilize a moderately dense beam in a proton plasma against the generation of waves drawing their energy from the differential streaming motion of the beam [Gomberoff, 2003]. We now examine the general case of both left-hand and right-hand pump waves and their effects on beam instability as a function of pump wave amplitude and frequency, beam speed, and plasma component temperatures. We find that the left-hand pump wave always gives beam stability above a threshold amplitude. Larger threshold trend with increasing beam speed and lower ones with increasing temperature. It is also shown that they can stabilize left-hand polarized instabilities in the case of large drift velocities. The right-hand pump similarly suppresses beam instabilities when its pump frequency is below the linearly unstable range of frequencies. However, when its pump frequency is within the range of instability, that part of the range below the pump frequency is stabilized beyond a threshold amplitude, but the part above becomes even more unstable in the presence of a right-hand pump.
Journal of Physics: Conference Series
Journal of Physics: Conference Series
We solved numerically the Vlasov-Maxwell system of equations for a bounded cylindrical and radial... more We solved numerically the Vlasov-Maxwell system of equations for a bounded cylindrical and radial inhomogeneous plasma which is confined by a strong magnetic field directed along the axis cylinder. Through this solution we found numerically the radial structure of the axial electric field corresponding to the high frequency fundamental transverse magnetic mode propagating in the cylindrical wave guide. Our result shows that the intensity of the electric field tends to be higher in those regions where the plasma is denser and also the field presents oscillations with intensities that decrease and vanish at the radial plasma boundary. This behavior could be relevant in the design of efficient modern plasma based particle accelerators that use the axial electric field to achieve this task.
We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. ... more We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. We show that the presence of a finite amplitude left-hand polarized wave produces electrostatic instabilities above a threshold amplitude. These instabilities occur when the phase velocities of the counter-streaming ion acoustic waves become equal, due to the action of the nonlinear wave. They do not exist in the absence of large-amplitude waves. We examine their growth rates and threshold amplitude behavior as a function of the beam speed, temperature, and large-amplitude wave frequency.
Physica B: Condensed Matter, 2016
Revista De Ciencias, Mar 1, 2015
Resumen Las estrellas de neutrones son objetos compactos remanentes en las explosiones de superno... more Resumen Las estrellas de neutrones son objetos compactos remanentes en las explosiones de supernovas. Observaciones astronómicas sugieren que el campo magnético superficial de estas estrellas decae en escalas largas de tiempo, proceso que debe ser mediado por efectos disipativos tales como la difusión lineal Ohmica. Aunque es bien sabido que las escalas de tiempo de la difusión Ohmica son mucho más largas que la edad del Universo, procesos no lineales como la difusión ambipolar o el efecto Hall pueden generar estructuras de pequeña escala que acortarían las escalas de tiempo [1]. En este artículo se ilustra el cálculo de los modos de difusión Ohmica confinados en la corteza esférica de estrellas de neutrones bajo simetría axial (2D). La solución de las ecuaciones diferenciales parciales del modelo se basa en un método espectral que expande las funciones angulares en polinomios de Legendre mientras que la parte radial y temporal se resuelve por separación de variables.
The Astrophysical Journal, 2014
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying... more In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are "Hall equilibria", i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an attractor state through adjacent stable configurations, around which damped oscillations occur. For this field, the decay scales with the Ohmic timescale. We also study the case of an unstable equilibrium consisting of both poloidal and toroidal field components that are confined within the crust. This field evolves into a stable configuration, which undergoes damped oscillations superimposed on a slow evolution towards an attractor, just as the purely poloidal one.
2011 Abstracts IEEE International Conference on Plasma Science, 2011
ABSTRACT form only given. We study the effect of the ambipolar diffusion (joint transport of magn... more ABSTRACT form only given. We study the effect of the ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term evolution of a magnetic field one dimensional configuration. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays or ionization-recombination processes. We show numerically that ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic-field gradients with associated current sheets around those regions where the magnetic field is weak. These results could have applications in explaining relevant processes promoting the magnetic field evolution inside neutron stars (particularly magnetars), magnetic field evolution in the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores.
The Astrophysical Journal, 2013
Magnetic protection of potentially habitable planets plays a central role in determining their ac... more Magnetic protection of potentially habitable planets plays a central role in determining their actual habitability and/or the chances of detecting atmospheric biosignatures. We develop here a thermal evolution model of potentially habitable Earth-like planets and super-Earths. Using up-to-date dynamo scaling laws we predict the properties of core dynamo magnetic fields and study the influence of thermal evolution on their properties. The level of magnetic protection of tidally locked and unlocked planets is estimated by combining simplified models of the planetary magnetosphere and a phenomenological description of the stellar wind. Thermal evolution introduces a strong dependence of magnetic protection on planetary mass and rotation rate. Tidally locked terrestrial planets with an Earth-like composition would have early dayside magnetospause distances between 1.5 and 4.0 R p , larger than previously estimated. Unlocked planets with periods of rotation ∼ 1 day are protected by magnetospheres extending between 3 and 8 R p. Our results are robust against variations in planetary bulk composition and uncertainties in other critical model parameters. For illustration purposes the thermal evolution and magnetic protection of the potentially habitable super-Earths GL 581d, GJ 667Cc and HD 40307g were also studied. Assuming an Earth-like composition we found that the dynamos of these planets are already extinct or close to being shut down. While GL 581d is the best protected, the protection of HD 40307g cannot be reliably estimated. GJ 667Cc, even under optimistic conditions, seems to be severely exposed to the stellar wind and, under the conditions of our model, has probably suffered massive atmospheric losses.
Physics of Plasmas, 2005
ABSTRACT
Monthly Notices of the Royal Astronomical Society, 2010
We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic... more We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term behavior of a non-uniform magnetic field in a one-dimensional geometry. Our main focus is the dissipation of magnetic energy inside neutron stars (particularly magnetars), but our results have a wider application, particularly to the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays (or ionization-recombination processes). In the "weak-coupling" limit of infrequent inter-particle interactions, the evolution of the magnetic field is controlled by the beta decay rate and can be described by a nonlinear partial integro-differential equation. In the opposite, "strong-coupling" regime, the evolution is controlled by the inter-particle collisions and can be modelled through a non-linear diffusion equation. We show numerically that, in both regimes, ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic field gradients with associated current sheets around those regions where the magnetic field is weak.
Journal of Geophysical Research, 2005
It is shown that ion-acoustic waves propagating along an external magnetic field and generated by... more It is shown that ion-acoustic waves propagating along an external magnetic field and generated by parametric decays of circularly polarized finite amplitude waves have the properties of ion-acoustic waves observed in the solar wind.
Journal of Geophysical Research, 2004
We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. ... more We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. We show that the presence of a finite amplitude left-hand polarized wave produces electrostatic instabilities above a threshold amplitude. These instabilities occur when the phase velocities of the counter-streaming ion acoustic waves become equal, due to the action of the nonlinear wave. They do not exist in the absence of large-amplitude waves. We examine their growth rates and threshold amplitude behavior as a function of the beam speed, temperature, and large-amplitude wave frequency.
We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic... more We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term behavior of a non-uniform magnetic field in a one-dimensional geometry. Our main focus is the dissipation of magnetic energy inside neutron stars (particularly magnetars), but our results have a wider application, particularly to the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays (or ionization-recombination processes). In the "weak-coupling" limit of infrequent inter-particle interactions, the evolution of the magnetic field is controlled by the beta decay rate and can be described by a nonlinear partial integro-differential equation. In the opposite, "strong-coupling" regime, the evolution is controlled by the inter-particle collisions and can be modelled through a non-linear diffusion equation. We show numerically that, in both regimes, ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic field gradients with associated current sheets around those regions where the magnetic field is weak.
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying... more In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are “Hall equilibria”, i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an attractor ...
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying... more In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are "Hall equilibria", i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an ...
Neutron stars are compact objects remaining of supernova explosions. Astronomical observations su... more Neutron stars are compact objects remaining of supernova explosions. Astronomical observations suggest that surface star magnetic fields decay over long dissipative time scales. Although it is well known that the diffusive time scales are much longer than the age of the universe, non linear processes such as ambipolar diffusion or Hall effect can generate small-scale structures that shorten the time scales [1]. In this paper we calculate the magnetic diffusion modes confined in spherical neutron star crusts with axial symmetry (2D). The solution of the partial differential equations is based on a spectral method that expands the angular functions in Legendre polynomials while the radial and temporal part are solved by separation of variables.
American Journal of Physics, 2020
We provide a guide to implementing the particle-in-cell algorithm, which is useful for simulating... more We provide a guide to implementing the particle-in-cell algorithm, which is useful for simulating diverse phenomena in plasmas. We focus on two-dimensional systems which have vector fields with three Cartesian components but depend only on two spatial coordinates. We describe the algorithm in detail, including particle-to-grid interpolation, the fast Fourier transform, the Boris algorithm, and the use of dimensionless units. As an example, we discuss a simulation of the two-stream instability, which occurs in a plasma system composed of two counter-streaming electrons and an ion background at rest.We provide a guide to implementing the particle-in-cell algorithm, which is useful for simulating diverse phenomena in plasmas. We focus on two-dimensional systems which have vector fields with three Cartesian components but depend only on two spatial coordinates. We describe the algorithm in detail, including particle-to-grid interpolation, the fast Fourier transform, the Boris algorithm, and the use of dimensionless units. As an example, we discuss a simulation of the two-stream instability, which occurs in a plasma system composed of two counter-streaming electrons and an ion background at rest.
We present here a comprehensive model for the evolution of the magnetic properties of habitable t... more We present here a comprehensive model for the evolution of the magnetic properties of habitable terrestrial planets (Earth-like planets, M ∼ 1 M ⊕ and super-Earths M ∼ 1 − 10 M ⊕) and their effects on the long-term protection against the atmospheric erosive action of stellar wind. Using up-to-date thermal evolution models and dynamo scaling laws we predict the evolution of the planetary dipole moment as a function of planetary mass and rotation rate. Combining these results with models for the evolution of the stellar wind, stellar XUV fluxes and exosphere properties of highly irradiated planets, we determine the properties of the planetary magnetosphere and the expected scale height of the atmosphere that together determine the level of thermal and non-thermal atmospheric mass losses. We have used this model to evaluate the early magnetic protection of the Earth and the already discovered potentially habitable super-Earths GJ 667Cc, Gl 581d and HD 85512b. We confirm that Earth-like planets, even under the highest attainable dynamo-generated magnetic field strengths, will lose a significant fraction of their atmospheres or their content of critical volatiles (e.g. H 2 O) if they are tidally locked in the HZ of dM stars. Planets in this mass-range with N/O-rich atmospheres, even under the best conditions of magnetic protection, will probably lose their atmospheres or their water content if they are in habitable zones closer than ∼ 0.8 AU (M ⋆ 0.7 − 0.9M ⊙). Super-Earths M p 3M ⊕ seem to have better chances of preserving their atmospheres even if they are tidally locked around dM stars. Under similar conditions of thermal and magnetic field evolution there seems to exist a planetary mass-dependent inner limit inside the HZ itself, below which large atmospheric mass-losses in super-Earths are expected. With the nominal value of the physical parameters in our conservative model this limit is, for example, ∼0.1 AU for 4M ⊕ and ∼0.04 AU for 8M ⊕. Under these conditions we predict that the atmosphere of GJ 667Cc has probably already been obliterated and it is presently uninhabitable. On the other hand, our model predicts that the atmospheres of Gl 581d and HD 85512b would be well protected by dynamo-generated magnetic fields even under the worst expected conditions of stellar aggression.
Journal of Geophysical Research, 2003
In a previous paper, sufficiently large-amplitude and left-handed ''pump waves'' propagating para... more In a previous paper, sufficiently large-amplitude and left-handed ''pump waves'' propagating parallel to the background magnetic field were shown to stabilize a moderately dense beam in a proton plasma against the generation of waves drawing their energy from the differential streaming motion of the beam [Gomberoff, 2003]. We now examine the general case of both left-hand and right-hand pump waves and their effects on beam instability as a function of pump wave amplitude and frequency, beam speed, and plasma component temperatures. We find that the left-hand pump wave always gives beam stability above a threshold amplitude. Larger threshold trend with increasing beam speed and lower ones with increasing temperature. It is also shown that they can stabilize left-hand polarized instabilities in the case of large drift velocities. The right-hand pump similarly suppresses beam instabilities when its pump frequency is below the linearly unstable range of frequencies. However, when its pump frequency is within the range of instability, that part of the range below the pump frequency is stabilized beyond a threshold amplitude, but the part above becomes even more unstable in the presence of a right-hand pump.
Journal of Physics: Conference Series
Journal of Physics: Conference Series
We solved numerically the Vlasov-Maxwell system of equations for a bounded cylindrical and radial... more We solved numerically the Vlasov-Maxwell system of equations for a bounded cylindrical and radial inhomogeneous plasma which is confined by a strong magnetic field directed along the axis cylinder. Through this solution we found numerically the radial structure of the axial electric field corresponding to the high frequency fundamental transverse magnetic mode propagating in the cylindrical wave guide. Our result shows that the intensity of the electric field tends to be higher in those regions where the plasma is denser and also the field presents oscillations with intensities that decrease and vanish at the radial plasma boundary. This behavior could be relevant in the design of efficient modern plasma based particle accelerators that use the axial electric field to achieve this task.
We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. ... more We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. We show that the presence of a finite amplitude left-hand polarized wave produces electrostatic instabilities above a threshold amplitude. These instabilities occur when the phase velocities of the counter-streaming ion acoustic waves become equal, due to the action of the nonlinear wave. They do not exist in the absence of large-amplitude waves. We examine their growth rates and threshold amplitude behavior as a function of the beam speed, temperature, and large-amplitude wave frequency.
Physica B: Condensed Matter, 2016
Revista De Ciencias, Mar 1, 2015
Resumen Las estrellas de neutrones son objetos compactos remanentes en las explosiones de superno... more Resumen Las estrellas de neutrones son objetos compactos remanentes en las explosiones de supernovas. Observaciones astronómicas sugieren que el campo magnético superficial de estas estrellas decae en escalas largas de tiempo, proceso que debe ser mediado por efectos disipativos tales como la difusión lineal Ohmica. Aunque es bien sabido que las escalas de tiempo de la difusión Ohmica son mucho más largas que la edad del Universo, procesos no lineales como la difusión ambipolar o el efecto Hall pueden generar estructuras de pequeña escala que acortarían las escalas de tiempo [1]. En este artículo se ilustra el cálculo de los modos de difusión Ohmica confinados en la corteza esférica de estrellas de neutrones bajo simetría axial (2D). La solución de las ecuaciones diferenciales parciales del modelo se basa en un método espectral que expande las funciones angulares en polinomios de Legendre mientras que la parte radial y temporal se resuelve por separación de variables.
The Astrophysical Journal, 2014
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying... more In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are "Hall equilibria", i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an attractor state through adjacent stable configurations, around which damped oscillations occur. For this field, the decay scales with the Ohmic timescale. We also study the case of an unstable equilibrium consisting of both poloidal and toroidal field components that are confined within the crust. This field evolves into a stable configuration, which undergoes damped oscillations superimposed on a slow evolution towards an attractor, just as the purely poloidal one.
2011 Abstracts IEEE International Conference on Plasma Science, 2011
ABSTRACT form only given. We study the effect of the ambipolar diffusion (joint transport of magn... more ABSTRACT form only given. We study the effect of the ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term evolution of a magnetic field one dimensional configuration. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays or ionization-recombination processes. We show numerically that ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic-field gradients with associated current sheets around those regions where the magnetic field is weak. These results could have applications in explaining relevant processes promoting the magnetic field evolution inside neutron stars (particularly magnetars), magnetic field evolution in the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores.
The Astrophysical Journal, 2013
Magnetic protection of potentially habitable planets plays a central role in determining their ac... more Magnetic protection of potentially habitable planets plays a central role in determining their actual habitability and/or the chances of detecting atmospheric biosignatures. We develop here a thermal evolution model of potentially habitable Earth-like planets and super-Earths. Using up-to-date dynamo scaling laws we predict the properties of core dynamo magnetic fields and study the influence of thermal evolution on their properties. The level of magnetic protection of tidally locked and unlocked planets is estimated by combining simplified models of the planetary magnetosphere and a phenomenological description of the stellar wind. Thermal evolution introduces a strong dependence of magnetic protection on planetary mass and rotation rate. Tidally locked terrestrial planets with an Earth-like composition would have early dayside magnetospause distances between 1.5 and 4.0 R p , larger than previously estimated. Unlocked planets with periods of rotation ∼ 1 day are protected by magnetospheres extending between 3 and 8 R p. Our results are robust against variations in planetary bulk composition and uncertainties in other critical model parameters. For illustration purposes the thermal evolution and magnetic protection of the potentially habitable super-Earths GL 581d, GJ 667Cc and HD 40307g were also studied. Assuming an Earth-like composition we found that the dynamos of these planets are already extinct or close to being shut down. While GL 581d is the best protected, the protection of HD 40307g cannot be reliably estimated. GJ 667Cc, even under optimistic conditions, seems to be severely exposed to the stellar wind and, under the conditions of our model, has probably suffered massive atmospheric losses.
Physics of Plasmas, 2005
ABSTRACT
Monthly Notices of the Royal Astronomical Society, 2010
We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic... more We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term behavior of a non-uniform magnetic field in a one-dimensional geometry. Our main focus is the dissipation of magnetic energy inside neutron stars (particularly magnetars), but our results have a wider application, particularly to the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays (or ionization-recombination processes). In the "weak-coupling" limit of infrequent inter-particle interactions, the evolution of the magnetic field is controlled by the beta decay rate and can be described by a nonlinear partial integro-differential equation. In the opposite, "strong-coupling" regime, the evolution is controlled by the inter-particle collisions and can be modelled through a non-linear diffusion equation. We show numerically that, in both regimes, ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic field gradients with associated current sheets around those regions where the magnetic field is weak.
Journal of Geophysical Research, 2005
It is shown that ion-acoustic waves propagating along an external magnetic field and generated by... more It is shown that ion-acoustic waves propagating along an external magnetic field and generated by parametric decays of circularly polarized finite amplitude waves have the properties of ion-acoustic waves observed in the solar wind.
Journal of Geophysical Research, 2004
We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. ... more We study the effect of a large-amplitude left-hand polarized wave on ion acoustic instabilities. We show that the presence of a finite amplitude left-hand polarized wave produces electrostatic instabilities above a threshold amplitude. These instabilities occur when the phase velocities of the counter-streaming ion acoustic waves become equal, due to the action of the nonlinear wave. They do not exist in the absence of large-amplitude waves. We examine their growth rates and threshold amplitude behavior as a function of the beam speed, temperature, and large-amplitude wave frequency.